Common easy open end closures for beer and beverage containers have a central or center panel that has a frangible panel (sometimes called a “tear panel,” “opening panel,” or “pour panel”) defined by a score formed on the outer surface, the “consumer side,” of the end closure. Popular “ecology” can ends are designed to provide a way of opening the end by fracturing the scored metal of the panel, while not allowing separation of any parts of the end. For example, the most common such beverage container end has a tear panel that is retained to the end by a non-scored hinge region joining the tear panel to the reminder of the end, with a rivet to attach a leverage tab provided for opening the tear panel. This type of container end, typically called a “stay-on-tab” (“SOT”) end has a tear panel that is defined by an incomplete circular-shaped score, with the non-scored segment serving as the retaining fragment of metal at the hinge-line of the displacement of the tear panel.
The container is typically a drawn and ironed metal can, usually constructed from a thin sheet of aluminum or steel. End closures for such containers are also typically constructed from a cut-edge of thin sheet of aluminum or steel, formed into a blank end, and manufactured into a finished end by a process often referred to as end conversion. These ends are formed in the process of first forming a cut-edge of thin metal, forming a blank end from the cut-edge, and converting the blank into an end closure which may be seamed onto a container. Although not presently a popular alternative, such containers and/or ends may be constructed of plastic material, with similar construction of non-detachable parts provided for openability.
One goal of the can end manufacturers is to provide a buckle resistant end. U.S. Pat. No. 3,525,455 (the '455 patent) describes a method aimed at improving the buckle strength of a can end having a seaming curl, a chuck wall, and a countersink along the peripheral edge of a center panel. The method includes forming a fold along at least substantially the entire length of the chuck wall. The fold has a vertical length that is approximately the same length as the seaming curl, and a thickness that is approximately equal to the length of the remaining chuck wall wherein the fold is pressed against the interior sidewall of the container when the end is seamed to the container's open end.
Another goal of the manufacturers of can ends is to reduce the amount of metal in the blank end which is provided to form the can end while at the same time maintaining the strength of the end. One method aimed at achieving this goal is described in U.S. Pat. No. 6,065,634 (the '634 patent). The '634 patent is directed to a can end member having a seaming curl, a chuck wall extending downwardly from the seaming curl to a countersink which is joined to a center panel of the can end. The method of the '634 patent reduces the amount of metal by reducing the cut edge of the blank. This is accomplished by increasing the chuck wall angle from approximately 11–13 degrees to an angle of 43 degrees.
The method of the '634 patent may decrease the diameter of the center panel. This could reduce area on the center panel that is needed for written instructions, such as opening instructions or recycling information. It may also restrict the size of the tear panel. Furthermore, because the angle of the chuck wall is increased, the space between the perimeter of the can end and the tear panel is increased. This could cause spillage during pouring and/or drinking.
The method of the '634 patent also produces a countersink. The '455 patent shares this aspect. The countersink is provided in the can end to improve strength However, because the countersink is a narrow circumferential recess, dirt will often collect within the countersink. Additionally, the dirt is often difficult to rinse away due to the geometry of the countersink.
U.S. Pat. No. 5,950,858 (the '858 patent) also discloses a method of strengthening a can end. The '858 patent discloses a can end having a countersink and a folded portion located at the junction of the center panel or within the countersink at the lowermost portion of the countersink. One of the stated benefits of Sergeant is that the fold provides effective resistance against the countersink inverting.